Recently, with the development of mobile devices such as smartphones, tablet PCs, and the like, thinning and slimming of a substrate for a display is required. As a display window or a front window of the mobile device, glass or tempered glass having excellent mechanical properties is generally used. However, glass causes a high weight of the mobile devices because it is heavy, and may be damaged by external impact.
Thus, plastic resin is being studied as a material for replacing the glass. A plastic resin film is suitable for the tendency to seek lighter mobile devices because it is light-weighted and may not be easily broken. Particularly, to achieve a film having high hardness and abrasion resistance, a film having a hard coating layer on a resin substrate has been suggested.
However, if the thickness of a previously known hard coating film is increased to achieve sufficient surface hardness to replace glass, wrinkles or curls may increase due to cure shrinkage of a hard coating layer, and cracks or peeling of a hard coating layer may be easily generated, and thus optimum properties may not be easily achieved or the field of application is limited.
Further, if the thickness of a hard coating film is made thin with the recent thinning and slimming trend of a substrate for a display, scratch resistance or strength of the hard coating film may not be sufficiently maintained, and thus, optimum properties may not be easily achieved or the field of application is limited.
Recently, studies on self-healing coating materials are actively progressing because they do not require an additional coating or repair process even if a surface is damaged, and they are extremely favorable for appearance of a product and performance maintenance. As a result of these studies, an UV curable composition using self-healing oligomers and a composition to which inorganic particles or fluorinated compounds are added to improve scratch resistance and anti-pollution, and the like have been introduced, but coating materials obtained therefrom may not have sufficient surface hardness and self-healing capability.
Recently, it has been introduced that if a coating material including a polyrotaxane compound is used, a self-healing coating membrane or coating film may be provided, and various methods are being attempted to apply the polyrotaxane compound to coating of automobiles, electronic products, and the like to commercialize it.
For example, WO2005-080469 describes substituting hydroxyl groups of a cyclic molecule α-cyclodextrin with hydroxypropyl groups or at a high substitution rate of methyl groups to improve properties of polyrotaxane.
WO2002-002159 describes crosslinking cyclic molecules (α-cyclodextrin) of polyrotaxane using polyethylene glycol.
WO2007-026578 describes a method for preparing polyrotaxane that can be dissolved in toluene or ethyl acetate by substituting hydroxyl groups of α-cyclodextrin with hydrophobic groups of ε-caprolactone, and WO2010-092948 and WO2007-040262 describe paint including polyrotaxane wherein hydroxyl groups of α-cyclodextrin are substituted by hydrophobic groups of ε-caprolactone.
WO2009-136618 describes polyrotaxane wherein a part or all of the hydroxyl groups of the cyclic molecule α-cyclodextrin are substituted by residues of an organic halogen compound to form a radical polymerization initiation part.
However, coating materials using previously known polyrotaxane compounds do not have sufficient mechanical properties required for a coating material such as scratch resistance, chemical resistance, and abrasion resistance, or do not have sufficient self-healing capability to scratches or external damage, and thus have limitations in commercialization.